Why dry raisins placed in water swell up?

When raisins are kept in water for a few hours, the raisins will swell up or they will expand in size. This happens due to osmosis, which is the movement of water molecules from a region of lower solute concentration to higher solute concentration through a semi or selectively permeable membrane.

Osmosis can be of two types, endosmosis (the entering of solvent from high to low concentration) and exosmosis (the flow of solvent from high to low concentration)

So when raisins are kept in water, the raisins has less solvent concentration (more solute concentration) and the water has comparatively more solvent concentration (less solute concentration), which means that it will act as a Hypotonic Solution. The raisins will act as a semi permeable membrane and water will move from the outer surroundings into the raisins (endosmosis) due to which the raisin will increase in size or swell up.

EXPLANATION: Diffusion is a process that moves things from where they are more concentrated to where they are less concentrated. Diffusion is the process that moves things in and out of the cell. Osmosis is important because it allows water, to move in and out of the cell. Hence, Osmosis is the diffusion of water. Cells have a cell membrane, which kind of like a shell, that holds the parts of a cell together and controls what moves in and out of the cell. Raisins and grapes are the same fruit. A raisin is a dehydrated grape. Raisins swells up when placed in hypotonic solution and dry up when places in hypertonic solution.